Using sulfur colloid particles the size of bacteria and tagged with 99mTc we have developed a tracer technique to evaluate urinary tract deterioration in patients with urinary tract infections. How and why these particles remain in the kidneys rather than descend to the bladder after reflux as does refluxed fluid is being evaluated in rabbits. Serial 197 Hg chlormerodrin Anger Camera scans are being serially performed on dogs over a period of months. Individual renal function studies are also being performed using insulin, PAH, and creatinine. The accuracy of this study to evaluate the clearance of each kidney will be determined. One renal unit will then be damaged and the studies repeated to see how accurately changing renal function can be monitored with this technique.